Lab 5 - ECE 421L 

  

Authored by Do Le (led2@unlv.nevada.edu)

23rd of September, 2020

  

Lab Description

    The purpose of this week's lab is to design CMOS inverters.

    A CMOS inverter can be created using an NMOS and PMOS MOSFETs.

    For the lab, we created two inverters. One with a 48µm width PMOS

    and 24µm width NMOS, and one  with a 12µm width PMOS and a 6µm width NMOS.

    The length for all four MOSFET was 600nm.

 

    The inverters are simulated for the output voltage driving capacitive loads. Simulations were done for each

    inverter driving 100fF, 1pF, 10pF, and 100pF loads. The simulations were done using both 

    the spectre simulator and the UltraSim simulator.

  

Prelab

    The pre-lab follows tutorial 3, and follows the creation of the 12µm/6µm NMOS/PMOS width

    inverter. Here is the schematic view of the inverter.

12u/6u Schematic

  

    I then created a layout with properly labeled pins so that the schematic can be LVS'd.

12u6u Layout

12u6u LVS  
 

Lab

48µm/24µm Inverter:

    The inverter is drafted similar to how the 12µm/6µm inverter is. Here is the schematic (Notice the multiplier).

48u24u Schematic

   

 

    Here is the layout. Because a 48µm wide PMOS is impractical, a 4 finger PMOS was used.

48u24u Layout

48u24u LVS

 

Simulations:

    Next the inverters are simulated while driving capacitive loads of 100fF, 1pF, 10pF, and 100pF.

    Here, the spectre simulator is used. This is the test schematic used for all of the simuations.

Simulation Schematic

 

    These are the results showing the 100fF, 1pF, 10pF, and 100pF simulations

    respective from left to right and top to bottom.

    

Spectre Simulation:

    12µm/6µm:

12u6u spectre 100f12u6u spectre 1p

12u6u spectre 10p12u6u spectre 100p

   

    48µm/24µm:

48u24u spectre 100f48u24u spectre 1p

48u24u spectre 10p48u24u spectre 100p

 

UltraSim Simulation:

    Next, the simulations were repeated using UltraSim.

 

 

    12µm/6µm:

12u6u UltraSim 100f12u6u UltraSim 1p

12u6u UltraSim 10p12u6u UltraSim 100p

 

    48µm/24µm:

48u24u UltraSim 100f48u24u UltraSim 1p

48u24u UltraSim 10p48u24u UltraSim 100p

 

Results:

    Looking at the results of the simulation, it can be noted that the 48µm/24µm takes a shorter amount of time to reach 5V than

    the 12µm/6µm. This is likely because the wider MOSFETs have a lower resistance, attributed to it's wider channel.

    As a result, the RC time constant is lower for the wider MOSFETs, allowing them to switch faster. 

  

Files:

    The cells done in this lab can be found here: lab5_dvl.zip.

 

That concludes lab 5.

 

   

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